Lactic acid, its salts, and esters have long been used as food additives and in various chemical and pharmaceutical applications. More recently, lactic acid has been used as a replacement for present plastic materials in the making of biodegradable polymers as well as in various other new uses where biodegradability is needed or desired, such as for medical implants and slow-release drugs. Accordingly, there is an ever-increasing demand for improved and economically viable lactic acid production processes. The present invention provides substantial improvements over conventional lactic acid production processes that employ fermentation.
The production of lactic acid is commonly carried out using fermentation by means of micro-organisms such as bacteria, yeasts and fungi. The fermentation substrate consists of carbohydrates together with suitable mineral and proteinaceous nutrients. After fermentation, the lactate and lactic acid-containing fermentation products must be separated from the biomass. These lactic acid-containing fermentation products are in the liquid form (i.e., liquid or in solution). Usually the biomass is separated from the lactate and lactic acid-containing fermentation products by means of filtration, centrifuging, flocculation, coagulation, flotation, or combinations thereof. Such a conventional process is described in WO 01/38283, wherein a continuous process for the preparation of lactic acid by means of fermentation is described. When the fermentation is carried out using bacteria, biomass separation is particularly difficult. Because of the small solid particles in the biomass, filtration per se is not possible.
In U.S. Pat. No. 5,453,365 the pH of a calcium or magnesium lactate fermentation broth is increased by means of ammonia and carbon dioxide addition in order to form ammonium lactate and cause precipitation of calcium carbonate or magnesium carbonate. The cellular material is adsorbed on the calcium carbonate or magnesium carbonate and for the most part precipitated therewith. The solids are subsequently separated by means of a filter or centrifuge.
WO 98/58072 describes the flocculation of biological material from organic acid-containing systems, more particularly ammonium acrylate systems. Flocculation here is caused by the addition of an anionic particulate material.
In U.S. Pat. No. 5,766,439 a method is described for biomass removal by microfiltration.